poj 1753 Flip Game（枚举）

枚举所有情况，每个位置可能变也可能不变，复杂度O(2^16)。

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 1 /*

 2 Author:Zhaofa Fang

 3 Lang:C++

 4 */

 5 #include <cstdio>

 6 #include <cstdlib>

 7 #include <iostream>

 8 #include <cmath>

 9 #include <cstring>

10 #include <algorithm>

11 #include <string>

12 #include <utility>

13 #include <vector>

14 #include <queue>

15 #include <stack>

16 #include <map>

17 #include <set>

18 using namespace std;

19 typedef long long ll;

20 #define pii pair<int,int>

21 #define pb push_back

22 #define mp make_pair

23 #define fi first

24 #define se second

25 #define lowbit(x) (x&(-x))

26 #define INF 2147483647;

27 

28 int tot,ans;

29 int a[17];

30 char str[17][17];

31 void change(int x)

32 {

33     a[x]^=1;

34     if(x-4>0)

35     {

36         a[x-4]^=1;

37     }

38     if(x-1>0 && (x-1)%4)

39     {

40         a[x-1]^=1;

41     }

42     if(x+1<17 && x%4)

43     {

44         a[x+1]^=1;

45     }

46     if(x+4<17)

47     {

48         a[x+4]^=1;

49     }

50 }

51 bool check()

52 {

53     int cnt=0;

54     for(int i=1;i<=16;i++)cnt+=a[i];

55     if(cnt % 16 == 0)return true;

56     else return false;

57 }

58 int tmp[17];

59 void dfs(int cur)

60 {

61     if(cur > 16)

62     {

63         if(check())

64         {

65             if(tot < ans)ans = tot;

66         }

67         return;

68     }

69     dfs(cur+1);

70     change(cur);tmp[tot]=cur;

71     tot++;

72     dfs(cur+1);

73     tot--;

74     change(cur);

75 

76 }

77 int main()

78 {

79     #ifndef ONLINE_JUDGE

80     freopen("in","r",stdin);

81     #endif

82     int len=0;

83     for(int i=0;i<4;i++)

84     {

85         scanf("%s",str[i]);

86         for(int j=0;j<4;j++)

87         if(str[i][j] == 'b')a[++len]=1;

88         else a[++len]=0;

89     }

90     tot=0;ans=(1<<16);

91     dfs(1);

92     if(ans != (1<<16))printf("%d\n",ans);

93     else puts("Impossible");

94     return 0;

95 }